1. Field of the Invention
The present invention is directed to an apparatus for injecting glue in joints and hair checks of wood, for instance for gluing loose knots in wooden boards.
2. Description of the Prior Art
When softwood boards of spruce, pine, or larch, or hardwood boards of maple or beech, are dried, hair checks are formed and the knots become loose due to shrinking. Those loose knots which do not drop out immediately after drying are likely to splinter during further processing, such as planing. Very knotty boards are therefore almost worthless and can be used or traded only as low-grade wood.
Known devices are directed to gluing such loose knots in the board by injecting glue at an overpressure into the gap between knot and board (see e.g. Swiss Patent No. 645,057, German OS 3,316,235 and U.S. Pat. No. 2,335,528). However, these devices are relatively bulky, and require that the glue injection head must be kept forcefully pressed against the wood surface, since otherwise the glue would escape from the sides of the injection head. The bulk and force inherent in such devices causes damage to wood surfaces, and the devices can be used only as stationary machines in which the board must be placed between the glue and injection head mounted on the upper portion of a frame and a supporting surface provided therebeneath.
U.S. Pat. No. 2,346,879 discloses apparatus for pressing cement into cracks of concrete slabs, in which the injection pressure is produced by a percussion device. The cement to be injected is introduced into a chamber, the bottom of which is formed with an injection opening to be placed onto the concrete slab, and the top of which is defined by a membrane which is struck by a percussion piston of a percussion device. The impact pulse acting on the membrane causes the cement to be ejected at high pressure from the injection opening of the chamber bottom. This apparatus is in no way related to the problems of injecting glue into wood surfaces, and furthermore has only a very small injection opening, and would be unsuitable for gluing loose knots in boards.